There are already lots of minimal PE examples on this board.

; Beer - example of tiny (one section) Win32 program

format PE GUI 4.0

include 'win32a.inc'

; no section defined - fasm will automatically create .flat section for both
; code and data, and set entry point at the beginning of this section

        invoke  MessageBoxA,0,_message,_caption,MB_ICONQUESTION+MB_YESNO
        cmp     eax,IDYES
        jne     exit

        invoke  mciSendString,_cmd_open,0,0,0
        invoke  mciSendString,_cmd_eject,0,0,0
        invoke  mciSendString,_cmd_close,0,0,0

exit:
        invoke  ExitProcess,0

_message db 'Do you need a place for the beer?',0
_caption db 'Desktop configuration',0

_cmd_open db 'open cdaudio',0
_cmd_eject db 'set cdaudio door open',0
_cmd_close db 'close cdaudio',0

; import data in the same section

data import

 library kernel32,'KERNEL32.DLL',\
         user32,'USER32.DLL',\
         winmm,'WINMM.DLL'

 import kernel32,\
        ExitProcess,'ExitProcess'

 import user32,\
        MessageBoxA,'MessageBoxA'

 import winmm,\
        mciSendString,'mciSendStringA'

end data    

There used to be this simple example in the fasmw package, which assembles to 1024 bytes:

Code:

; Beer - example of tiny (one section) Win32 program

format PE GUI 4.0

include 'win32a.inc'

; no section defined - fasm will automatically create .flat section for both
; code and data, and set entry point at the beginning of this section

        invoke  MessageBoxA,0,_message,_caption,MB_ICONQUESTION+MB_YESNO
        cmp     eax,IDYES
        jne     exit

        invoke  mciSendString,_cmd_open,0,0,0
        invoke  mciSendString,_cmd_eject,0,0,0
        invoke  mciSendString,_cmd_close,0,0,0

exit:
        invoke  ExitProcess,0

_message db 'Do you need a place for the beer?',0
_caption db 'Desktop configuration',0

_cmd_open db 'open cdaudio',0
_cmd_eject db 'set cdaudio door open',0
_cmd_close db 'close cdaudio',0

; import data in the same section

data import

 library kernel32,'KERNEL32.DLL',\
         user32,'USER32.DLL',\
         winmm,'WINMM.DLL'

 import kernel32,\
        ExitProcess,'ExitProcess'

 import user32,\
        MessageBoxA,'MessageBoxA'

 import winmm,\
        mciSendString,'mciSendStringA'

end data    

I stopped distributing it in the official package though, partly because AVs seemed to hate it more than the others. Also: it relies on an obsolete technology (CD tray).